The present invention relates to a lithium secondary battery which makes it possible to produce a highly reliable battery in particular preferably to be used for driving a motor of an electric vehicle, etc. at low processing costs.
In recent years, while it is eagerly desired to regulate the emission of exhaust gas including carbon dioxide and other harmful substances with the elevation of environment protection campaign as a background, in the automobile industry, in replacement of automobiles using fossil fuels, such as a vehicle driven by gasoline, the campaign to promote introduction of an electric vehicle (EV) and a hybrid electric vehicle (HEV) has become active.
A lithium secondary battery as a motor-driving battery acting as a key for putting such EV as well as HEV into practical use, is required to have such characteristics as large battery capacity as well as high battery output. Here, large battery capacity means that an absolute value of energy to be stored becomes larger, thus measures must be planned so that the safety at the time of handling as well as charging and discharging may be secured. In addition, for the purpose of obtaining higher output, it is necessary to make the internal resistance of a battery, that is, a value of resistance between a positive output terminal and a negative output terminal, smaller.
Therefore, by making the battery""s capacity large, volume per a unit battery, namely the battery size, must be inevitably made larger, and, to a battery case to be used in accordance with this, such mechanical characteristics as well as electric characteristics that secure the above described safety and output are requested.
Here, as for a battery case for a small-sized lithium secondary battery, etc., a case with one-end sealing produced by deep drawing is used as the battery case, but in the case where battery size has been made larger, there is a disadvantage that it is technologically difficult to produce a case by way of deep drawing, and in addition, resulting in highly costs to be incurred.
In addition, as described later, as for a wound-type internal electrode body, it is preferable that current collecting tabs for the positive pole should be connected to one end of the internal electrode body, and current collecting tabs for the negative pole should be connected to the other end thereof respectively from the viewpoint of securing the safety, but in the case where a case with one-end sealing has been used, there was a problem that it was difficult to connect to the case with a plurality of current collecting tabs which have been connected at the time of winding at one end.
The present invention was made by contemplating the problems of the prior art mentioned above. That is, according to the present invention, there is provided a lithium secondary battery, comprising: an internal electrode body including a positive electrode, a negative electrode, and a separator, the positive electrode and the negative electrode being wound via the separator so that the positive electrode and the negative electrode are not brought into direct contact with each, other,
organic electrolyte, and
a battery case containing the internal electrode body;
wherein a pipe is used as the battery case.
In such a lithium secondary battery of the present invention, from the viewpoint of safety, it is preferable that the pipe is arranged to be electrically neutral. In addition, it is preferable that at least one end of the pipe is subjected to cramping processing, with which forming of an external output terminal, etc. becomes easier. Of course, it is especially preferable that both ends of the pipe are subjected to the cramping processing. Moreover, it is preferable to provide a necking portion at an end of the pipe having been subjected to the cramping processing, and is preferable to provide bursting mechanism at least at one end of the battery. With this arrangement, for example, even in the case where the bursting mechanism provided in the battery case has operated as a result of increase in battery""s internal pressure due to short circuit having taken place between a positive and a negative electrode of the battery, popping out of the internal electric body from the open portion in the bursting mechanism is prevented.
In addition, if a positive output terminal is arranged to be formed at one end of a battery, and a negative output terminal is arranged to be formed at the other end of the battery, reduction in battery""s internal resistance can be planned and preferable since not only is production of battery is simple but also the battery case does not have to be a current path. And, as a material for the battery case, aluminum or aluminum alloy, or stainless steel is preferably selected.
Incidentally, the characteristics of the above described lithium secondary battery of the present invention are preferably adopted as a lithium secondary battery with battery capacity of not less than 5 Ah, and the lithium secondary battery of the present invention is preferably used for an electric vehicle (EV) or for a hybrid electric vehicle (HEV).